Metals have conventionally been melted, utilizing large loads and large furnaces for so doing. Current state-of-the-art metal melting furnaces include electric arc furnaces, cupola furnaces, blast furnaces, induction furnaces, and crucible or pot furnaces.
Electric arc furnaces are lined with refractories for containing molten metal. Such refractories slowly decompose and are removed with slag, which floats atop the molten metal. Metal to be melted is charged into the furnace with additives to make recovery of slag easier. Heat is provided with electric arcs from three carbon or graphite electrodes. Such furnaces are commonly used in the steel industry, primarily for scrap metal melting because they may be used in decentralized mini-mills that produce items for local markets instead of larger centralized mills.
Cupola furnaces are the oldest type of furnaces used in foundries. Alternating layers of metal and ferrous alloys, coke, and limestone are fed into the furnace from the top. Limestone is added to react with impurities in the metal and floats atop the melt as it melts to protect the metal from oxidation. Cupola furnaces are typically used for melting cast iron or grey iron.
Blast furnaces are extremely large cylinders lined with refractory brick. Iron ore, coke and limestone are dumped into the top of the blast furnace as preheated air is blown into the bottom. The chemical reactions that occur extract the iron from the ore. Once a blast furnace is started, it will run continuously for 4-10 years with only short stops to perform planned maintenance.
Reverberatory or hearth furnaces are used in batch melting of non-ferrous metals. A reverberatory furnace is a special type of hearth furnace in which the material under treatment is heated indirectly by means of a flame deflected downwardly from the roof. Hearth furnaces are used to produce small quantities of metal, usually for specialty alloys.
Induction furnaces are either “coreless” or “channel” type. Coreless melting furnaces use a refractory envelope to contain the metal. The envelope is surrounded by a copper coil carrying alternating current. Operating on the same basis as a transformer, the metal charge in the furnace works like a single secondary terminal, thereby producing heat through eddy current flow when power is applied to the multi-turn copper primary coil. When the metal melts, the electromagnetic forces also produce a stirring action. In an induction channel furnace, a channel is formed in the refractory through the coil, and thus a channel forms a continuous loop with the metal in the main part of the furnace. The hot metal in the channel circulates in the main body of the metal in the furnace envelope and is replaced by a colder metal. Unlike the coreless induction furnace, a source of primary molten metal is required for a startup of a channel furnace.
A crucible or pot furnace is a melting furnace that uses a ceramic crucible to contain the molten metal. The crucible is heated by electric resistant heating elements or by a natural gas flame. Insulation surrounds the crucible to retain heat. Typically, the entire apparatus can be tipped to pour the molten metal into a mold.
All of the existing furnaces consume more energy to melt metal than what is deemed desirable. Additionally, the prior art devices have many safety risks. Other shortcomings include contamination of the melt from materials of construction of the containment, limitations on melt temperatures and requirements for large facilities requiring significant capital costs.